This invention relates to liquid fuel pumping apparatus for supplying fuel to internal combustion engines, the apparatus being of the kind comprising an injection pump operable in timed relationship with an associated engine, a fuel control rod movable to effect adjustment of the quantity of fuel supplied at each injection stroke, governor mechanism including a governor weight which is driven at a speed dependent upon the speed of the associated engine, a member movable by the weight, a governor spring for opposing movement of the member as the speed of the engine increases, operator adjustable means for adjusting the force exerted by the spring and link means connecting said member with the fuel control rod whereby for a given setting of the operator adjustable means, as the engine speed increases, the fuel control rod will be moved to reduce the amount of fuel supplied by the apparatus.
Such apparatus is well known, and there is usually incorporated in the governor mechanism a maximum fuel stop which can be temporarily put out of action to allow the supply of a larger or excess quantity of fuel for starting purposes. The movement of the control rod to effect this adjustment is achieved by firstly moving the maximum fuel stop and secondly by the operator moving the operator adjustable means in a direction to increase the force exerted by the governor spring.
In some forms of apparatus, the procedure described above is not effective to move the fuel control rod to the excess fuel position. This is because, in some forms of apparatus, an additional spring is interposed between the governor spring and said member and the movement of the end of the governor spring which is effectively connected to said additional spring, is limited by a stop. The action of the additional spring is to modify the fuel delivery of the apparatus. The additional spring is a relatively light spring, and is unable to provide sufficient force to effect movement of the fuel control rod to the excess fuel position when the maximum fuel stop is temporarily put out of action.
In other forms of apparatus, an adjustable fuel stop is provided and its position is determined by means of a device in one example, responsive to the pressure of air supplied to the engine air inlet manifold. The device incorporates a strong spring the force of which, even when the additional spring and stop mentioned in the proceeding paragraph is not provided, cannot be overcome by the governor spring. Even with apparatus of the kind specified, it is sometimes difficult to ensure that under all conditions the fuel control rod can be moved to the excess fuel position in the manner described.